Production method of alloy member, alloy member, and product using alloy member

ABSTRACT

A production method for an alloy member having mainly high hardness and high resistance to corrosion and produced by an additive manufacturing method, the alloy member, and a product using the alloy member are provided. The production method for an alloy member includes: an additive manufacturing step of forming a shaped member through an additive manufacturing method using an alloy powder containing elements Co, Cr, Fe, Ni, and Ti each in a range of 5 atom% to 35 atom% and containing Mo in a range exceeding 0 atom% and 8 atom% or less, the remainder being unavoidable impurities; and a heat treatment step of holding the shaped member in a temperature range higher than 500° C. and lower than 900° C. directly after the additive manufacturing step without undergoing a step of holding the shaped member in a temperature range of 1080° C. to 1180° C.

TECHNICAL FIELD

The present invention relates to a production method of an alloy memberproduced through an additive manufacturing method, an alloy memberobtained through this production method, and a product using the alloymember.

BACKGROUND ART

In recent years, high-entropy alloys (HEAs) have been proposed as alloysof a new technical idea different from alloys (for example, alloysobtained by adding trace amounts of plural kinds of sub-componentelements to 1 to 3 kinds of main component elements) of technical ideasin the related art. HEAs are defined as alloys consisting of 5 or morekinds of principal metal elements (respectively 5 to 35 atom%), and areknown to exhibit characteristics (a) to (d) below. In addition, an alloyconcept of a multi-principal element alloy (MPEA) having a plurality ofprincipal elements and allowing existence of multiple phases has alsobeen proposed. In the present application, HEAs and MPEAs are treated asthe same concept, and both are collectively referred to as HEAs.

Examples of advantages of HEAs include (a) stabilization of a mixedstate due to a negative increase in a mixed entropy term in the Gibbsfree energy equation, (b) a diffusion delay due to a complex finestructure, (c) a decrease in temperature dependence, which is amechanical property, or an increase in hardness due to high latticestrain caused by the difference in sizes of constituent atoms, and (d)an improvement in corrosion resistance due to a complex effect (alsoreferred to as a cocktail effect) due to coexistence of variouselements.

Here, Patent Literature 1 discloses an alloy member containing elementsCo, Cr, Fe, Ni, and Ti each in a range of 5 atom% or more to 35 atom% orless and containing Mo in a range exceeding 0 atom% and 8 atom% or less,the remainder being unavoidable impurities, in which minute particleshaving an average particle diameter of 100 nm or less are dispersed andprecipitate in parent phase crystal grains.

According to Patent Literature 1, it is thought that a fine structure inwhich minute particles are dispersed and precipitate in parent phasecrystal grains is obtained by subjecting a shaped member producedthrough an additive manufacturing method to a predetermined heattreatment, and as a result, an alloy member having improved tensilestrength, significantly improved ductility, and improved corrosionresistance can be provided.

CITATION LIST Patent Literature

[Patent Literature 1]

PCT International Publication No. WO 2019/031577

SUMMARY OF INVENTION Technical Problem

According to the technique of Patent Literature 1, an alloy memberhaving excellent corrosion resistance and mechanical properties such astensile strength or ductility can be obtained. However, furtherimprovement in hardness is required to apply this alloy member to asevere environment where wear resistance is required.

As described above, an objective of the present invention is to providean alloy member which is produced through an additive manufacturingmethod using an alloy powder, has excellent corrosion resistance andmechanical properties, and has wear resistance due to further improvedhardness, and a production method thereof. In addition, anotherobjective of the present invention is to provide a production method ofan alloy member having higher mechanical properties. Furthermore, stillanother objective of the present invention is to provide a producthaving excellent corrosion resistance and wear resistance and excellentmechanical properties using this alloy member.

Solution to Problem

A production method of an alloy member of the present invention is aproduction method of an alloy member including: an additivemanufacturing step of forming a shaped member through an additivemanufacturing method using an alloy powder containing elements Co, Cr,Fe, Ni, and Ti each in a range of 5 atom% or more to 35 atom% or lessand containing Mo in a range exceeding 0 atom% and 8 atom% or less, theremainder being unavoidable impurities (the shaped member obtainedthrough such a step is regarded as a shaped member A); and an aging heattreatment step of holding the shaped member (shaped member A) obtainedthrough the shaping step in a temperature range higher than 500° C. andlower than 900° C. in a state where a melt solidification structure isprovided at least in a surface layer part.

A production method of an alloy member according to another aspect ofthe present invention is a production method of an alloy memberincluding the following steps between the additive manufacturing stepand the aging heat treatment step: a solution heat treatment step ofheating the shaped member (shaped member A) formed through the additivemanufacturing step and holding the shaped member in a temperature rangeof 1080° C. or more to 1180° C. or less; a cooling step of cooling theshaped member after the solution heat treatment step (a shaped memberobtained through such a step is regarded as a shaped member B); and thena remelting and resolidifying step of melting and solidifying thesurface layer part of the shaped member (shaped member B) again (ashaped member obtained through such a step is regarded as a shapedmember C).

A production method of an alloy member according to still another aspectof the present invention is a production method of an alloy memberincluding the following steps between the additive manufacturing stepand the aging heat treatment step: a solution heat treatment step ofheating the shaped member (shaped member A) and holding the shapedmember in a temperature range of 1080° C. or more to 1180° C. or less; acooling step of cooling the shaped member after the solution heattreatment step (a shaped member obtained through such a step is regardedas a shaped member B); and then a surface layer-adding and shaping stepof forming a melt solidification layer on the surface layer part of theshaped member (shaped member B) that has undergone the cooling step,through the additive manufacturing method using the alloy powder (ashaped member obtained through such a step is regarded as a shapedmember D).

An alloy member according to the present invention is an alloy memberincluding: elements Co, Cr, Fe, Ni, and Ti each in a range of 5 atom% ormore to 35 atom% or less; Mo in a range exceeding 0 atom% and 8 atom% orless; and unavoidable impurities as a remainder, in which the alloymember comprises a microcell structure with an average particle diameterof 10 µm or less at least in crystal grains of a surface layer part, aboundary part of the microcell structure has a dislocation having asurface density higher than that inside the microcell structure, andultrafine particles having an average particle diameter of 50 nm or lessare dispersed and precipitate at least inside the microcell structure.

The present invention is a product using the above-described alloymember. This product may be an impeller of a fluid machine, a screws ofan injection molding machine, or a die.

Advantageous Effects of Invention

According to the present invention, an alloy member having excellentcorrosion resistance and mechanical properties and having wearresistance due to improved hardness, and a production method of the samecan be provided. In addition, a production method of an alloy memberhaving higher mechanical properties can be provided. Furthermore, aproduct having excellent corrosion resistance and wear resistance andexcellent mechanical properties using this alloy member can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process diagram illustrating an example of a productionmethod of an alloy member according to the present invention.

FIG. 2 is a cross-sectional schematic diagram illustrating an example ofan additive manufacturing method and a configuration of an additivemanufacturing device of a selective laser melting method.

FIG. 3 is a cross-sectional schematic diagram illustrating an example ofan additive manufacturing method and a configuration of an additivemanufacturing device of a laser metal deposition method.

FIG. 4 is a graph illustrating an example of an aging heat treatmentstep after the additive manufacturing step.

FIG. 5 shows scanning electron microscope images (SEM images) (a) and(b) and scanning transmission electron microscope images (STEM images)(c) and (d) illustrating an example of a fine structure of a first alloymember according to the present invention.

FIG. 6 shows a scanning electron microscope image (SEM image) (a) and ascanning transmission electron microscope image (STEM image) (b)illustrating an example of a fine structure of an alloy member accordingto a comparative example.

FIG. 7 is a process diagram illustrating another example of a productionmethod of an alloy member according to the present invention.

FIG. 8 is a process diagram illustrating still another example of aproduction method of an alloy member according to the present invention.

FIG. 9 is a schematic diagram illustrating an example of across-sectional view of a fine structure of a second alloy member (ashaped member C or a shaped member D) according to the presentinvention.

FIG. 10 is a graph illustrating a relationship between the hardness andthe aging heat treatment temperature according to the present invention.

DESCRIPTION OF EMBODIMENTS Basic Idea of Present Invention

First, the present inventors or the like have conducted extensivestudies on an alloy composition and a shape control method to develop ahigh-entropy alloy member having excellent shape controllability andductility without sacrificing the characteristics of high-entropy alloys(HEAs). As a result, by forming an additively manufactured memberthrough an additive manufacturing method using a powder of aCo-Cr-Fe-Ni-Ti-Mo alloy, an alloy member having excellent tensilestrength, ductility, and corrosion resistance and having better shapecontrollability than an ordinarily forged HEA member in the related artcan be obtained. That is, it is determined that a fine structure inwhich minute particles having an average particle diameter of 100 run orless are dispersed and precipitate is formed by conducting a solutionheat treatment at 1080° C. or more to 1180° C. or less to significantlyimprove both the tensile strength and the ductility. Specifically, ithas been confirmed that a near net shape alloy member having favorablemechanical properties (for example, a tensile strength of 1,100 MPa ormore and a breaking elongation of 10% or more) can be obtained. Inaddition, it has been confirmed that the alloy member also exhibits ahigh pitting corrosion generating potential and has excellent corrosionresistance. However, it has been found that, when a wear resistance testis performed for a mechanical device in which this alloy member is used,it is desirable for the alloy member to have further improved wearresistance, that is, improved hardness under severe conditions such asuse in a sliding part. The alloy member in the present invention is ametal additively manufactured member produced through an additivemanufacturing method (also referred to as an additive productionmethod), and is sometimes simply referred to as a shaped member below.

Therefore, the present inventors or the like have repeatedlyinvestigated and studied the relationship between variouscharacteristics and a fine structure of an alloy member derived from theproduction method. As a result, they have found that the hardness can beimproved by performing an aging treatment step (referred to as an agingheat treatment in the present invention) of holding the shaped member(hereinafter referred to as a shaped member A), which has been shaped,in a temperature range higher than 500° C. and lower than 900° C. in astate where a melt solidification structure is provided at least in asurface layer part without undergoing a solution heat treatment, at1080° C. or more and 1180° C. or less, and have come up with the presentinvention. This point is the basic common idea of the present invention.As a result of investigating the mechanism for improving the hardness,it has been confirmed that a cell-shaped region (referred to as amicrocell structure in the present invention) having an average particlediameter of 10 (µm or less which is finely divided by a network ofdislocations having a higher density than the surroundings is generatedinside crystal grains consisting of columnar crystals produced throughan additive manufacturing method and that ultrafine particles having anaverage particle diameter of 50 µm or less which are smaller than minuteparticles in parent phase crystal grains other than the microcellstructure are generated in the microcell structure through an aging heattreatment. Here, the dislocations are linear crystal defects containedin a crystal and are sites where an atomic arrangement is locallychanged. It is thought that the hardness is increased by generation ofnanoscale ultrafine particles with high-density dislocations. Thesedislocations can be identified by observation through various kinds ofelectron microscopy (for example, transmission electron microscopy (TEM)and scanning transmission electron microscopy (STEM)).

As described above, a first embodiment of the production method of analloy member of the present invention is as follows.

(i) A shaped member A is obtained through an additive manufacturingmethod using an alloy powder containing elements Co, Cr, Fe, Ni, and Tieach in a range of 5 atom% or more to 35 atom% or less, Mo in a rangeexceeding 0 atom% and 8 atom% or less, and unavoidable impurities as aremainder to subject the shaped member A to an aging heat treatment inwhich the shaped member A is held in a temperature range higher than500° C. and lower than 900° C. in a state where a melt solidificationstructure is provided at least in a surface layer part. That is, thepresent invention is characterized in that the shaped member which hasbeen additively manufactured is directly subjected to an aging heattreatment without undergoing a solution heat treatment step, whereby thehardness is improved. Although the ductility of this alloy member islower than in the case of undergoing a solution heat treatment step, thealloy member has excellent tensile strength. In addition, the alloymember also has excellent corrosion resistance and is also particularlysuitable for applications requiring wear resistance due to improvedhardness. This point is different from Patent Literature 1.

The basic of the production method of the present invention is asdescribed above. However, as another production method of the presentinvention, there is an aspect of additionally carrying out a new meltingand solidifying step on a preliminarily obtained shaped member.

(ii) As a second embodiment, the preliminarily obtained shaped member Ais subjected to a solution heat treatment of holding the temperature at1080° C. or more to 1180° C. or less. Accordingly, a structure in whichminute particles having an average particle diameter of 50 nm to 100 nmare dispersed and precipitate in parent phase crystal grains is formed,and a shaped member B having improved mechanical properties is obtained.Thereafter, a shaped member C (hereinafter sometimes referred to as aremelted and reshaped member C) obtained by the surface layer part ofthe shaped member B is melted and solidified again using a laser beam orthe like is obtained. Thereafter, the shaped member C is subjected tothe above-described aging heat treatment in a state where a meltsolidification structure is provided at least in the surface layer part,and ultrafine particles having an average particle diameter of 50 nm orless which are smaller than the minute particles in the parent phasecrystal grains are dispersed and precipitate in a microcell structure ofthe surface layer part to impart hardness. Therefore, according to thisembodiment, in addition to the first embodiment, it is possible toobtain an alloy member having higher mechanical properties and improvedhardness of the surface layer part.

(iii) As a third embodiment, an additive manufacturing method (additiveremanufacturing step) is carried out on the shaped member Bpreliminarily obtained in the above-described method in (ii) to obtain ashaped member D (hereinafter sometimes referred to as a surfacelayer-added and shaped member D) obtained by forming a new meltsolidification layer in the surface layer part of the shaped member B.Thereafter, the shaped member D is subjected to the above-describedaging heat treatment in a state where a melt solidification structure isprovided at least in the surface layer part, and ultrafine particleshaving an average particle diameter of 50 nm or less which are smallerthan the minute particles in the parent phase crystal grains aredispersed and precipitate in a microcell structure of the surface layerpart to impart hardness. Therefore, according to this embodiment, it isalso possible to obtain an alloy member having higher mechanicalproperties and improved hardness of the surface layer part.

In the above-described production methods in (ii) and (iii), anadditional melting and solidifying step is selectively performed on apreliminarily obtained (produced) shaped member. The remelted andreshaped member C in the second embodiment (ii) and the surfacelayer-added and shaped member D in the third embodiment (iii) havecommon points with the shaped member A in the first embodiment (i) inthat they are solidified structures in which a microcell structure isprovided in at least a surface layer part and an aging heat treatment isperformed without undergoing a solution treatment. Such productionmethods correspond to the production methods for an alloy member havinghigher mechanical properties in the present invention. According tothese production methods, it is possible to selectively manufacturealloy members according to applications such as an application requiringmainly high wear resistance or an application requiring not only wearresistance but also mechanical properties. Accordingly, as theproduction process is shortened, the variety of products is expanded,which is beneficial for production management.

In addition, the following improvements or changes can be made in theabove-described production method of an alloy member.

(iv) A laser beam or an electron beam can be used as a heat source usedin the additive manufacturing method in the additive manufacturing stepand the additive remanufacturing step. Accordingly, additivemanufacturing can be performed in an inert gas atmosphere or in avacuum. Therefore, mixing of impurities due to an atmosphere such asoxygen or nitrogen in an alloy member can be reduced.

(v) As a material supply method of the additive manufacturing method inthe additive manufacturing step and the additive remanufacturing step, asupply method using a powder bed and a direct metal deposition method,such as laser metal deposition method, in which a powder is directlyejected to a molten part can be used. Accordingly, it is possible todeal with both a shaping method having excellent degree of freedom inshape by a powder bed method and local shaping by a direct metaldeposition method.

In addition, the alloy member of the present invention is (vi) an alloymember including: elements Co, Cr, Fe, Ni, and Ti each in a range of 5atom% or more to 35 atom% or less; Mo in a range exceeding 0 atom% and 8atom% or less; and unavoidable impurities as a remainder, in which amicrocell structure with an average particle diameter of 10 µm or lessis provided at least in crystal grains of a surface layer part, aboundary part of the microcell structure has a dislocation having asurface density higher than that inside the microcell structure, andultrafine particles having an average particle diameter of 50 nm or lessare dispersed and precipitate at least inside the microcell structure.Having such a structure improves the hardness.

The following improvements or changes can be made in the above-describedalloy member.

(vii) Ti is concentrated in the boundary part of the microcell structureof the parent phase. When Ti with a large atomic radius is concentrated,the lattice distortion at an atomic level becomes larger than that ofthe surroundings, so that dislocations can more stably remain. Inaddition, an effect of further inhibiting the movement of dislocationscan also be expected by transforming at least a part of the concentratedTi into ultrafine particles or other intermetallic compounds through anaging heat treatment, which is effective for increasing the hardness.

(viii) The crystal structure of the parent phase has at least one of aface-centered cubic structure or a simple cubic structure. Such acrystal structure is effective for imparting ductility required as amatrix from the viewpoint of excellent deformability.

(ix) The alloy member has excellent hardness and can have a Vickershardness of 550 HV or more. In particular, the alloy members accordingto the above-described production methods (ii) and (iii) includes asurface layer part having a hardness of 550 HV or more on a maternalbody having a tensile strength of 1,100 MPa or more and a breakingelongation of 10% or more. A breaking elongation of 5% or more and atensile strength of 1,500 MPa or more can be obtained also through theproduction method (i). The corrosion resistance is also superior to thatof corrosion-resistant stainless steel. In this manner, these alloymembers have excellent mechanical properties and hardness.

Hereinafter, the embodiments of the present invention will be describedwith reference to the drawings according to the procedure of aproduction method. However, the present invention is not limited to theembodiments exemplified here, and can be appropriately combined andimproved within the scope not departing from the technical idea of theinvention.

Production Method of Alloy Member

FIG. 1 is a process diagram illustrating an example of a productionmethod of an alloy member according to an embodiment of the presentinvention. The production method of the present invention ischaracterized by an additive manufacturing step and an aging heattreatment step. Hereinafter, the embodiment of the present inventionwill be described in more detail for each step.

First, an alloy powder 20 having a desired HEA composition(Co-Cr-Fe-Ni-Ti-Mo) is prepared. The alloy powder 20 to be used can beobtained through, for example, an atomization method. There is noparticular limitation on the atomization method, and the conventionalmethods can be used. For example, gas atomization methods (such as avacuum gas atomization method and an electrode-induced dissolution typegas atomization method), centrifugal atomization methods (such as a diskatomization method and a plasma rotation electrode atomization method),and plasma atomization methods can be preferably used.

Chemical Composition

An HEA composition of the present invention contains 5 elements of Co,Cr, Fe, Ni, and Ti each in a range of 5 atom% or more to 35 atom% orless as main components and contains Mo in a range exceeding 0 atom% and8 atom% or less as sub-components, the remainder being unavoidableimpurities.

The chemical composition may contain 20 atom% or more and 35 atom% orless of Co, 10 atom% or more and 25 atom% or less of Cr, 10 atom% ormore and 25 atom% or less of Fe, 15 atom% or more and 30 atom% or lessof Ni, and 5 atom% or more and 15 atom% or less of Ti.

The chemical composition may contain 25 atom% or more and 33 atom% ofCo, 15 atom% or more and 23 atom% or less of Cr, 15 atom% or more and 23atom% or less of Fe, 17 atom% or more and 28 atom% or less of Ni, 5atom% or more and 10 atom% or less of Ti, and 1 atom% or more and 7atom% or less of Mo.

The chemical composition may contain 25 atom% or more and less than 30atom% of Co, 15 atom% or more and less than 20 atom% of Cr, 15 atom% ormore and less than 20 atom% of Fe, 23 atom% to 28 atom% of Ni, 7 atom%to 10 atom% of Ti, and 1 atom% to 7 atom% of Mo.

The chemical composition may contain 30 atom% or more and 33 atom% orless of Co, 20 atom% or more and 23 atom% or less of Cr, 20 atom% ormore and 23 atom% or less of Fe, 17 atom% or more and less than 23 atom%of Ni, 5 atom% or more and less than 7 atom% of Ti, and 1 atom% or moreand 3 atom% or less of Mo.

By controlling these composition ranges, it is more effective to achieveboth improvements in ductility and tensile strength.

In the composition ranges, in a case of prioritizing the improvement intensile strength, it is more preferable that the content of Co be 25atom% or more and less than 30 atom%, the content of Cr be 15 atom% ormore and less than 20 atom%, the content of Fe be 15 atom% or more andless than 20 atom%, the content of Ni be 23 atom% or more and 28 atom%or less, the content of Ti be 7 atom% or more and 10 atom% or less, andthe content of Mo be 1 atom% or more and 7 atom% or less.

In addition, in the composition ranges, in a case of prioritizing theimprovement in ductility, it is more preferable that the content of Cobe 30 atom% or more and 33 atom% or less, the content of Cr be 20 atom%or more and 23 atom% or less, the content of Fe be 20 atom% or more and23 atom% or less, the content of Ni be 17 atom% or more and less than 23atom%, the content of Ti be 5 atom% or more and less than 7 atom%, andthe content of Mo be 1 atom% or more and 3 atom% or less.

In the above-described composition ranges, as a composition particularlyhaving excellent tensile strength and ductility, the content of Co maybe 26.7 atom%, the content of Cr may be 17.9 atom%, the content of Femay be 17.9 atom%, the content of Ni may be 26.8 atom%, the content ofTi may be 8.9 atom%, and the content of Mo may be 1.8 atom% as in apowder P1 used in examples to be shown below. In addition, the contentof Co may be 28.0 atom%, the content of Cr may be 19.7 atom%, thecontent of Fe may be 17.6 atom%, the content of Ni may be 23.4 atom%,the content of Ti may be 8.9 atom%, and the content of Mo may be 2.4atom% as in a powder P2. Either composition corresponds to thecomposition ranges in the case of prioritizing the improvement in thetensile strength, but the composition of P2 can be set to have anincreased content of Co or Cr compared to P1 in consideration of theimprovement of ductility.

Powder Particle Diameter

The average particle diameter of the alloy powder 20 is preferably 10 µmor more and 200 µm or less from the viewpoint of handleability orfilling properties. Among these, a suitable average particle diameterdiffers depending on the additive manufacturing method used. An averageparticle diameter of 10 µm or more and 50 µm or less is more preferablein a selective laser melting (SLM) method and an average particlediameter of 45 µm or more and 105 µm or less is more preferable in anelectron beam melting (EBM) method. In addition, an average particlediameter of 50 µm or more and 150 µm or less may be set in a laser metaldeposition (LMD) method. If the average particle diameter is less than10 µm, the alloy powder 20 is likely to fly up in the next additivemanufacturing step, which may cause a decrease in the shape accuracy ofan additively manufactured body of an alloy. On the other hand, if theaverage particle diameter exceeds 200 µm, this may cause an increase inthe surface roughness of the additively manufactured body andinsufficient melting of the alloy powder 20 in the next additivemanufacturing step.

Additive Manufacturing Step

Next, an additive manufacturing step of forming an alloy additivelymanufactured body (hereinafter simply referred to as a shaped member)101 having a desired shape is performed through a metal powder additivemanufacturing method (hereinafter simply referred to as an additivemanufacturing method) in which the alloy powder 20 prepared above isused. A shaped member having a hardness equal to or higher than that ofa forging material and having a three-dimensional complex shape can beproduced by applying an additive manufacturing method that shapes a nearnet shape alloy member through melting and solidifying. Additivemanufacturing methods using an SLM method, an EBM method, and LMD methodcan be suitably used as the additive manufacturing method.

Hereinafter, an additive manufacturing step performed through an SLMmethod will be described. FIG. 2 is a schematic diagram illustrating aconfiguration of a powder additive manufacturing device 100 of the SLMmethod. A stage 102 is lowered by the thickness of one layer (forexample, about 20 to 50 µm) of a shaped member 101 to be additivelymanufactured. An alloy powder 105 is supplied from a powder supplycontainer 104 onto a base plate 103 on the upper surface of the stage102, and the alloy powder 105 is flattened by a recoater 160 to form apowder bed 107 (layered powder).

Next, unmelted powder on the base plate 103 is irradiated with a laserbeam 109 output from a laser oscillator 108 through a galvanometermirror 110 based on 2D slice data converted from 3D-CAD data of theshaped member 101 to be shaped, and a minute molten pool is formed,moved, and sequentially melted and solidified to form a 2D slice-shapedsolidification layer 112. The unmelted powder is collected in acollection container 111. Laminating is performed by repeating thisoperation to produce the shaped member 101.

Removal Step

The shaped member 101 is produced integrally with the base plate 103 andis covered with unmelted powder. At the time of removal, the unmeltedpowder is collected after the irradiation with a laser beam is completedand the powder and the shaped member 101 are sufficiently cooled, andthe shaped member 101 and the base plate 103 are removed from the powderadditive manufacturing device 100. Thereafter, the shaped member 101 iscut from the base plate 103 to obtain a shaped member 101 (correspondingto a shaped member A).

Here, a sample for observing a fine structure was collected from theremoved shaped member 101, and the fine structure of the sample wasobserved using a scanning electron microscope. As a result, the parentphase of the shaped member 101 had a structure (a so-called quenchedsolidification structure) in which fine columnar crystals (with anaverage width of 50 µm or less) stood together along a laminationdirection of the shaped member 101. Upon closer observation, microcellstructures with an average diameter of 10 µm or less were formed insidethe fine columnar crystals. Here, the microcell structures indicateelliptical or rectangular solidification structures that appear byelectrolytic etching or the like using oxalic acid or the like.

Next, an additive manufacturing step by a laser metal deposition method(LMD method) will be described.

FIG. 3 is a schematic diagram illustrating a configuration of a powderadditive manufacturing device 200 of the LMD method. An optical systemis focused on a surface layer part of a shaped member 303 to beadditively manufactured, and the alloy powder 105 is ejected andsupplied from a powder supply container 201 toward a laser focal part.

At the same time, the shaped member on a base plate 205 is irradiatedwith a laser beam or electron beam 203 output from a laser oscillator202 through a laser head part 206 based on an irradiation path convertedfrom 3D-CAD data of the shaped member 303 to be shaped, and a minutemolten pool is formed, moved, and sequentially melted and solidified toform a solidification layer 112 on the irradiation path. Solidificationlayers were laminated by advancing this operation along the irradiationpath to produce a shaped member 101 (corresponding to a shaped memberA). In a remelting and resolidifying step to be described below, amolten part can also be formed on the surface layer part by scanning alaser beam or an electron beam on the shaped member 303 without ejectingand supplying the alloy powder 105.

Aging Heat Treatment Step

An example of an aging heat treatment is shown in FIG. 4 . Theabove-described shaped member 101 is heated by raising the temperature,and an aging heat treatment of holding the shaped member in atemperature range in which the number of ultrafine particles easilyincreases, for example, in a temperature range higher than 500° C. andlower than 900° C. is conducted with the purpose of increasing thehardness of the shaped member. For example, in applications such aspumps and dies to be described below, a member with almost no decreasein hardness when used in a temperature range below the temperature of anaging heat treatment can be obtained by performing the aging heattreatment at a temperature or higher than the temperature at which ashaped member is used. Members that are required to have wear resistanceat a high temperature are preferably subjected to an aging heattreatment at a temperature or higher than the temperature at which theshaped members are used. In addition, when a surface treatment isapplied to impart wear resistance, the surface treatment temperature isoften high. In this case, an aging heat treatment is preferablyperformed at a temperature or higher than the surface treatmenttemperature. The temperature of an aging heat treatment for increasingthe hardness of an additively manufactured body is preferably 600° C. ormore and 850° C. or less and more preferably 650° C. or more and 800° C.or less. When the aging heat treatment temperature is higher than 500°C., an effect of improving the strength can be obtained. When the agingheat treatment temperature is lower than 900° C., formation of hexagonalprecipitates can be inhibited and the ductility can be maintained. Anupper limit value and a lower limit value can be arbitrarily combined.Similarly, the following numerical values can also be arbitrarilycombined. The holding time may be 0.5 hours or longer and 24 hours orshorter. The holding time is preferably set to 0.5 hours or longer and 8hours or shorter and more preferably set to 1 hour or longer and 8 hoursor shorter. When the holding time is 0.5 hours or longer, the effect ofimproving the strength can be obtained. When the holding time is 24hours or shorter, formation of hexagonal precipitates causingdeterioration in corrosion resistance can be inhibited. By the aboveaging heat treatment, nanoscale ultrafine particles having an averageparticle diameter of 50 nm or less can be generated in a microcellstructure to be described below, thereby improving the strength.

A cooling step after the aging heat treatment is not particularlylimited. However, there is a possibility that nanoscale ultrafineparticles may be excessively generated if the temperature is held nearthe aging heat treatment temperature for a long period of time.Therefore, the temperature may be cooled to room temperature through aircooling, gas cooling, or the like. In addition, FIG. 4 is merely anexample, and the heat treatment pattern can be variously changed. Inaddition, in the process of raising the temperature in the aging heattreatment, the retention temperature in an intermediate temperaturerange at which it is difficult to adjust the precipitation amount can beshortened if the rate of temperature increase is 5° C./minute or higher,which is suitable. The temperature rising rate is preferably 10°C./minute or higher. The upper limit is not particularly limited, but isabout 1000° C./minute or lower from the viewpoint of securingtemperature uniformity in the shaped member 101, particularly preventionof generation of an overheated part.

Ultrafine Particles

As described above, in the aging heat treatment of the presentinvention, ultrafine particles are generated in the microcell structurehaving an average diameter of 10 µm or less. The average particlediameter of the ultrafine particles is 50 nm or less which is smallerthan that of minute particles in parent phase crystal grains to bedescribed below. The lower limit of the average particle diameter is notparticularly limited, but is, for example, about 2 nm, preferably 3 nm,and more preferably 5 nm. The upper limit thereof is preferably about 30nm, more preferably 20 nm, and still more preferably 10 nm. In a casewhere the average particle diameter of ultrafine particles is 2 nm to 50nm, the hardness of a product can be increased. It has been found thatthe ductility of a product decreases in a case where the averageparticle diameter of ultrafine particles exceeds 50 nm. Regarding thesize of ultrafine particles, an image containing the ultraline particlesis acquired by high-magnification observation means represented bytransmission electron microscopy or high-resolution scanning electronmicroscopy, an average value of the diameters of inscribed circles andthe diameters of circumscribed circles of the ultrafine particles isused as a particle diameter of the ultrafine particles, and an averagevalue of particle diameters of 20 ultraline particles is used as anaverage particle diameter.

Fine Structure of Alloy Member

FIG. 5 illustrates an example of a fine structure of an alloy member(aging heat treatment material: M1-650AG) according to the presentinvention to be described below, in which (a) and (b) are scanningelectron microscope images (SEM images) and (c) and (d) are scanningtransmission electron microscope images (STEM images).

The alloy member of the present invention has a parent phase structure 2mainly composed of columnar crystals having a crystal grain size of 20µm or more and 150 µm or less (an average crystal grain size of 100 µmor less) (one structure is shown by a broken line because it isdifficult to distinguish them from this view) as shown in the SEM imageof (a). The average crystal grain size is an average grain size of 10crystal grains measured through a cutting method using an SEM image ofmagnification of 500 times. In addition, although not shown in the SEMimage of (a), microcell structures having an average diameter of 10 µmor less are formed inside the structure. It can be stated that, forexample, the interval indicated by the arrow in an enlarged image of (b)indicates a diameter of a microcell structure. Moreover, the enrichmentof Ti was confirmed in a boundary part 3 of the microcell structureshown by a white bright part in the SEM-EDS image of (b). In addition,in the high-magnification bright-field image of the STEM image of (c), abrighter region indicates the inside of the microcell structure and theboundary part 3 of the microstructure includes a dislocation 4 shown bya black line having a higher density than the inside of the microcellstructure. Accordingly, by confirming the concentration part where moreblack streaks are gathered compared to the inside of the microstructureusing the STEM image, it is possible to identify that there is adislocation having a higher surface density than the inside of thestructure. In addition, it was confirmed that a precipitate 5 containingan intermetallic compound is formed at the boundary part 3 of anothermicrocell structure. Furthermore, ultrafine particles 6 having anaverage particle diameter of about 3 nm were confirmed in thehigh-magnification STEM image of (d). In addition, an element mappingimage by STEM-EDX in this region is shown in the upper right of (d), andit was confirmed that the above-described ultrafine particles 6 wereparticles in which Ni and Ti were concentrated, (e) schematicallyillustrates a fine structure. As described above, this fine structurehas a microcell structure in crystal grains of a surface layer part, andthe boundary part 3 of this microcell structure has the blackstreak-like dislocation 4 having a higher surface density than theinside of the microcell structure. Furthermore, it was found that themicrocell structure is a structure in which the ultrafine particles 6are dispersed and precipitate.

On the other hand, FIG. 6 illustrates an example of a fine structure ofan alloy member (solution treatment material: M1-S) according to acomparative example to be described below, in which (a) is a scanningelectron microscope image (SEM image) and (b) is a scanning transmissionelectron microscope image (STEM image).

An alloy member M1 (without a solution heat treatment nor an aging heattreatment) of a comparative example has a parent phase crystal structuremainly composed of columnar crystals having crystal grain sizes of 20 µmto 150 µm (an average crystal grain size of 100 µm or less) similarly toFIG. 5 a and has microcell structures with an average diameter of 10 µmor less therein. In addition, M1-S (subjected to a solution heattreatment but no aging heat treatment) had a parent phase structure(crystal grain) 7 mainly composed of equiaxed crystals having crystalgrain sizes of 50 µm to 150 µm (average crystal grain size of 100 µm orless) as shown in FIG. 6 a . It was confirmed that columnar crystalswere recrystallized into equiaxed crystals through a solution heattreatment. In addition, as shown in FIG. 6 b , minute particles 8 havingan average particle diameter of 20 to 30 nm were observed in the parentphase crystal grains in M1-S. An element mapping image by STEM-EDX isalso shown in (b), and it was confirmed that the minute particles 8 wereparticles in which Ni and Ti were concentrated. In the alloy member M1,only the microcell structures having dislocations were seen, and noclear ultrafine particles having a particle diameter of 3 nm or morewere observed.

Production Method Including Remelting and Resolidifying Step

The above-described structure in which the microcell structure and theultrafine particles coexist is generated by directly subjecting a meltsolidification structure having a microcell structure to an aging heattreatment as it is. An outline of another production method utilizingthis characteristic will be described below.

The production method according to another embodiment of the presentinvention can be started by preparing a preliminarily obtained shapedmember A as shown in FIG. 7 . As the shaped member A, one obtained afterthe above-described removal step may be used, or one separately producedin advance may be used. A solution heat treatment described below isperformed on the shaped member A to obtain a shaped member B having aparent phase structure mainly composed of equiaxed crystals. The surfacelayer of this shaped member B is melted and solidified through a laserbeam or an electron beam to form a new solidification layer. Asdescribed above, a solidification layer can be formed by scanning alaser beam or an electron beam on the shaped member B without ejectingand supplying an alloy powder. Such a remelting and resolidifying stepis performed to obtain a remelted and reshaped member C. This remeltedand reshaped member C is obtained by forming a melt solidificationstructure containing a microcell structure having a diameter of 10 µm orless in a surface layer on a maternal body having excellent corrosionresistance and mechanical properties. By directly subjecting thisremelted and reshaped member C to an aging heat treatment, an alloymember having superior mechanical properties such as tensile strength orductility and improved hardness can be obtained.

Production Method Including Surface Layer-Adding and Shaping Step

An outline of still another production method of obtaining a structurein which ultrafine particles and a microcell structure according to thepresent invention coexist will be described.

As shown in FIG. 8 , this production method may be started by preparinga preliminarily obtained shaped member A or can also be started bypreliminarily preparing a shaped member B having a parent phasestructure mainly composed of equiaxed crystals due to a solution heattreatment. As the shaped member B, one obtained after the solution heattreatment step may be used, or one separately produced in advance may beused. The shaped member B is subjected to an additive manufacturingmethod using a laser or an electron beam, and a surface layer-adding andshaping step of forming a new solidification layer on a surface layerpart thereof through melting and solidifying is performed to obtain asurface layer-added and shaped member (shaped member D). By directlysubjecting this shaped member D to an aging heat treatment, an alloymember having superior mechanical properties such as tensile strength orductility and improved hardness can be obtained.

A second alloy member produced through the production method using theabove-described remelting and resolidifying step or the surfacelayer-adding and shaping step has a surface layer part with an improvedhardness. That is, as shown in FIG. 9 , a parent phase structure mainlycomposed of equiaxed crystals having excellent toughness and ductilitycan be arranged in an inside 101 a of an alloy member, and a structurewhere microcell structures coexist with ultrafine particles which aresmaller than minute particles contained in the inside 101 a of the alloymember can be provided in a surface layer part 101 b. Accordingly, asdescribed above, an alloy member having superior mechanical propertiessuch as tensile strength or ductility and improved hardness is obtained.

Soluble Heat Treatment

The solution heat treatment will be described below. The holdingtemperature in the solution heat treatment is in a temperature range of1080° C. to 1180° C. The holding temperature is preferably 1100° C. to1140° C. and more preferably 1110° C. to 1130° C. If the holdingtemperature is 1080° C. or higher, hexagonal precipitates leading toembrittlement are unlikely to precipitate and remain. In addition, ifthe holding temperature is 1180° C. or lower, defects such as partialmelting or coarsening of the crystal grain size are unlikely to occur.In addition, the holding time at the maximum temperature may be 0.5hours to 24 hours, preferably 0.5 hours to 8 hours, and more preferably1 hour to 4 hours. If the holding time is 0.5 hours or longer, theformation of hexagonal precipitates in the shaped member 101 can beinhibited. If the holding time is 24 hours or shorter, the coarsening ofthe crystal grain size can be inhibited.

In addition, in the temperature rising process in this solution heattreatment, if the rate of temperature increase in a temperature zone(for example, 800° C. to 1080° C.) in which hexagonal precipitates arelikely to be formed is set to be fast, for example, 5° C./minute orhigher, the amount of hexagonal precipitates can be reduced before theheat treatment, which is suitable. The temperature rising rate ispreferably 10° C./minute or higher. The upper limit is not particularlylimited, but is about 1000° C./minute from the viewpoint of securingtemperature uniformity in the shaped member 101, particularly preventionof generation of an overheated part. In the present invention, since thesolid solution limit of an alloy is unclear and minute particles havingan average particle diameter of 100 nm or less are dispersed andprecipitate in an alloy member which is a final product, theabove-described heat treatment can also be referred to as apseudo-solution heat treatment. However, in the present specification,this treatment is simply referred to as a solution heat treatment.

Cooling Step

Next, a cooling step is performed on a shaped member after the solutionheat treatment step. In the cooling step, it is preferable to performcooling at a cooling rate of 110° C./minute or more and 2400° C./minuteor less at least in the temperature range from a holding temperature to800° C. in a heat treatment. Here, the cooling step is performed at acooling rate of preferably 110° C./minute or higher and lower than 600°C./minute and more preferably 200° C./minute or higher and lower than600° C./minute. The cooling in this range can be adjusted by gas coolingusing inert gases, for example, nitrogen, argon, and helium. Inaddition, there is also an embodiment in which the cooling step isperformed at a cooling rate of 600° C./minute or more and 2400°C./minute or less and more preferably 1000° C./minute or more and 2000°C./minute or less. The cooling in this range can be adjusted by a liquidcooling using, for example, a salt bath, a quenching oil, and a aqueouspolymer solution. At a cooling rate of lower than 110° C./minute (forexample, furnace cooling or air cooling treatment), hexagonalprecipitates are likely to be produced from grain boundaries, which maycause a problem of deterioration in corrosion resistance. In addition,at a cooling rate of exceeding 2400° C./minute (for example, immersioncooling in a water tank), deformation of a shaped member due totemperature unevenness that occurs during rapid cooling may beproblematic. In addition, it is preferable to continue cooling even at atemperature of 800° C. or lower. For example, it is preferable tocontinuously perform cooling in a temperature range from 700° C. to roomtemperature at the above-described approximate cooling rate.

Application and Product

Applications and Products using the alloy member of the presentinvention are arbitrary. Mechanical properties and wear resistance canbe obtained according the applications by appropriately selecting aproduction method, for example, subjecting an additively manufacturedbody to an aging heat treatment and subjecting an additivelymanufactured body to a solution heat treatment and an aging heattreatment. In addition, a shaped member A or a shaped member B can beseparately produced and prepared. Since the shaped member A or theshaped member B can be appropriately used according to a desired productor production time, production management can be rationalized and theproduct can be produced at low cost.

Examples of applications include impellers of fluid machines, screws ofinjection molding machines, screws or cylinders of oil well drillingdevice or for injection molding, turbine wheels of generators or thelike, impellers of compressors, valves or joints of chemical plants,heat exchangers, pumps, semiconductor manufacturing devices or members,and various dies such as casting dies, forging dies, press dies, andplastic molding dies. In the present invention, these machines, devices,members, dies, part, and the like are collectively referred to asproducts.

EXAMPLES

Hereinafter, the present invention will be described more specificallywith reference to examples and comparative example. However, the presentinvention is not limited to these examples.

Experiment 1 Production of HEA Powders P1 and P2

Raw materials were mixed with each other according to the nominalcompositions shown in Table 1, and alloy powders were produced frommolten metal through a vacuum gas atomization method. Next, the obtainedalloy powders were classified using a sieve and sorted so that theparticle diameters were 10 µm or more and 53 µm or less and the averageparticle diameter (d50) was about 35 µm to prepare HEA powders P1 andP2. The reason why the compositions of P1 and P2 were selected isbecause they had excellent mechanical properties particularly relatingto strength and ductility in the preliminary studies by the inventors.Powders and the like having compositions disclosed in PCT InternationalPublication No. WO 2019/031577 described above can also be used, forexample.

TABLE 1 Nominal compositions (unit: atom%) of HEA powders P1 and P2 HEApowders Co Cr Fe Ni Ti Mo P1 26.7 17.9 17.9 26.8 8.9 1.8 P2 28.0 19.717.6 23.4 8.9 2.4

Experiment 2 Production of Alloy Members M1(M2), M1(M2)-500AG,M1(M2)-600AG, M1(M2)-650AG, M1(M2)-700AG, M1(M2)-800AG, M1(M2)-900AG,and M1(M2)-S

Regarding the HEA powder P1 prepared in Experiment 1, a shaped member M1(additively manufactured body: a prismatic material of 25 mm × 25 mm ×10 mm height, the height direction being a lamination direction) wasadditively manufactured through an SLM method according to the procedureof the additive manufacturing step of FIG. 1 using the powder additivemanufacturing device (EOS M290 manufactured by EOS) as shown in FIG. 2 .The laser output during the additive manufacturing was set to 300 Wbased on preliminary studies by the inventors, the laser scanning speedwas set to 1000 mm/second, and the scanning interval was set to 0.11 mm.In addition, the lamination thickness for each layer was set to about0.04 mm.

After an additive manufacturing step S30 and a removal step S50, theshaped member M1 (corresponding to the shaped member A) was obtained.This shaped member M1 was subjected to various heat treatments toproduce alloy members.

First, the shaped member M1 was subjected to an aging heat treatment asit was. In an aging heat treatment step S70, a sample obtained byincreasing the temperature at a rate of temperature increase of 10°C./minute and holding the temperature at 500° C. for 8 hours using avacuum furnace, and then performing cooling using high-pressure nitrogengas at a set pressure of 0.5 MPa was regarded as M1-500AG. Similarly,samples obtained by holding the temperature at 600° C., 650° C., 700°C., 800° C., and 900° C. for 8 hours, and then similarly performingcooling using nitrogen gas were regarded as M1-600AG, M1-650AG,M1-700AG, M1-800AG, and M1-900AG.

Next, the shaped member M1 was subjected to only a solution heattreatment. In the solution heat treatment step, a sample obtained byincreasing the temperature at a rate of temperature increase of 10°C./minute and holding the temperature at 1120° C. for 1 hour using avacuum furnace, and then performing cooling using high-pressure nitrogengas at a set pressure of 0.5 MPa was regarded as M1-S (corresponding tothe shaped member B).

Furthermore, regarding the HEA powder P2, a shaped member M2(corresponding to the shaped member A) was obtained through the additivemanufacturing step S30 and the removal step S50 in the same manner asabove. The aging heat treatment step S70 was performed on the shapedmember M2 to produce M2-500AG, M2-600AG, M2-650AG, M2-700AG, M2-800AG,and M2-900AG. In addition, only a solution heat treatment was performedon the shaped member M2 to produce M2-S (corresponding to the shapedmember B).

Production of Alloy Member M1(M2)-RM650AG

The previously obtained M1-S (corresponding to the shaped member B) wasirradiated with a laser beam under the same conditions as above withoutsupplying powder, and a remelting and resolidifying step S60 of meltingthe surface layer thereof by only one layer to shape a new meltsolidification layer was performed to obtain a shaped member(corresponding to the shaped member C). Thereafter, a sample obtained byperforming the aging heat treatment step S70 in which the temperaturewas increased at a rate of temperature increase of 10° C./minute, heldat 650° C. for 8 hours using a vacuum furnace, and then cooled usinghigh-pressure nitrogen gas at a set pressure of 0.5 MPa was regarded asM1-RM650AG. Furthermore, M2-RM650AG was produced by performing theremelting and resolidifying step S60 and the aging heat treatment stepS70 on M2-S in the same manner as above.

Production of Alloy Member M1(M2)-LD650AG

The previously obtained M1-S (corresponding to the shaped member B) wassubjected to a laser metal deposition method (LMD method) in which theP1 powder was used, and a surface layer-adding and shaping step S65 ofadditively manufacturing only one layer of a new melt solidificationlayer on a surface layer part thereof was performed to obtain a shapedmember (corresponding to the shaped member D). Regarding the shapingconditions, the laser output was set to 1.0 kW, the scanning speed wasset to 1000 mm/minute, the scanning interval was set to 2.0 mm, and theamount of powder supplied was set to 14 g/minute. Thereafter, a sampleobtained by performing the aging heat treatment step S70 in which thetemperature was increased at a rate of temperature increase of 10°C./minute, held at 650° C. for 8 hours using a vacuum furnace, and thencooled using high-pressure nitrogen gas at a set pressure of 0.5 MPa wasregarded as M1-LD650AG. Furthermore, M2-LD650AG was produced byperforming the surface layer-adding and shaping step S65 and the agingheat treatment step S70 on M2-S in the same manner as above using theHEA powder P2. Although the number of new melt solidification layers wasonly one here, lamination of two layers or more can be performed byperforming the same surface layer-adding and shaping step plural times.

Experiment 3 Observation of Fine Structure of Alloy Member

Test pieces for fine structure observation were collected from variousalloy members produced above, and the fine structure observation wasperformed through the above-described technique using various electronmicroscopes (SEM, STEM, and STEM-EDX) and an optical microscope.Production specifications of the alloy members and fine structureobservation results are shown in Table 2. In each sample, parent phasescontained FCC.

TABLE 2 Alloy member Powder Solution heat treatment Aging heat treatment(temperature × time) Crystal grain size (µm) Microcell structureMaternal body structure Cell diameter (µm) Ultrafine particle diameter(µm) Presence or absence of Ti concentration at boundary Minute particlediameter (µm) M1 P1 None None 40 2 - Present - M1-500AG 500° C. for 8hours 40 2 - Present - M1-600AG 600° C. for 8 hours 40 2 2 Present -M1-650AG 650° C. for 8 hours 40 2 3 Present - Ml-700AG 700° C. for 8hours 50 2 10 Present - M1-800AG 800° C. for 8 hours 85 3 30 Present -M1-900AG 900° C. for 8 hours 120 (Disappeared) 70 Absent - M1-S Done(1120° C. × 1 hour) None 80 (Disappeared) - Absent 80 M1-RM650AG 650° C.for 8 hours (Surface layer) 70 (Inside) 80 (Surface layer) 8 (Inside)disappeared (Surface layer) 10 (Surface layer) present (Inside) absent80 M1-LD650AG 650° C. for 8 hours (Surface layer) 70 (Inside) 80(Surface layer) 8 (Inside) disappeared (Surface layer) 10 (Surfacelayer) present (Inside) absent 80 M2 P2 None None 45 1 - Present -M2-500AG 500° C. for 8 hours 45 1 - Present - M2-600AG 600° C. for 8hours 45 1 3 Present - M2-650AG 650° C. for 8 hours 45 1 3 Present -M2-700AG 700° C. for 8 hours 45 1 3 Present - M2-800AG 800° C. for 8hours 95 2 25 Present - M2-900AG 900° C. for 8 hours 150 (Disappeared)80 Absent - M2-S Done (1120° C. × 1 hour) None 90 (Disappeared) - Absent50 M2-RM650AG 650° C. for 8 hours (Surface layer) 80 (Inside) 90(Surface layer) 8 (Inside) disappeared (Surface layer) 10 (Surfacelayer) present (Inside) absent 50 M2-LD650AG 650° C. for 8 hours(Surface layer) 80 (Inside) 90 (Surface layer) 8 (Inside) disappeared(Surface layer) 10 (Surface layer) present (Inside) absent 50 Note 1:Average values are shown for the crystal grain size, the cell diameter,and the ultrafine particle diameter. Note 2: The inside shows averagevalues of the crystal grain size and the minute particle diameter in ashaped body which becomes a maternal body.

As shown in Table 2, the parent phase structures of the alloy members M1and M2 which had not been subjected to an aging heat treatment had astructure (so-called locally quenched solidification structure) in whichfine columnar crystals having an average crystal grain size of 100 µm orless stood together along a lamination direction of additivelymanufactured bodies. The columnar crystals referred to herein aredefined as crystals in which the ratio of the major axis length of acrystal grain to the minor axis length is 2 or more. Microcellstructures having a diameter of 10 µm or less were formed inside crystalgrains. In addition, looking at M1-500AG, M1-600AG, M1-650AG, M1-700AG,M1-800AG, M1-900AG, M2-500AG, M2-600AG, M2-650AG, M2-700AG, M2-800AG,and M2-900AG obtained by subjecting these alloy members M1 and M2 to anaging heat treatment, although the parent phase structures weresubstantially composed of columnar crystals and had microcellstructures, the microcell structures disappeared during the aging heattreatment at 900° C. and the diameter of ultrafine particles in crystalgrains also exceeded 50 nm.

In addition, in M1-S and M2-S obtained by subjecting the alloy membersM1 and M2 to only a solution heat treatment, although ultrafineparticles in crystal grains precipitated, microcell structuresdisappeared and crystal grains were changed into polygonal equiaxedcrystals.

Furthermore, in M1-RM650AG and M2-RM650AG obtained by remelting surfacelayers of the alloy members M1-S and M2-S, to provide a new meltsolidification layer thereon, and further performing an aging heattreatment, although fine particles precipitated therein, microcellstructures disappeared and became equiaxed crystals. However, the meltsolidification layer on the surface layer was composed of columnarcrystals, had microcell structures, and also had ultrafine particlesprecipitating.

In addition, the same results were obtained for M1-LD650AG andM2-LD650AG obtained by providing a new melt solidification layer on thealloy members M1-S and M2-S through additive manufacturing and furtherperforming an aging heat treatment. It was confirmed by TEM and STEM-EDXthat minute particles having an average particle diameter of 100 nm orless were formed in the crystal grains inside the alloy members M1-S,M2-S, M1-RM650AG, M1-LD650AG, M2-RM650AG, and M2-LD650AG. Furthermore,it was confirmed by STEM-EDX that more Ni and Ti components wereconcentrated in the minute particles than in parent phase crystals.

Experiment 4 Measurement of Tensile Strength and Breaking Elongation

M1, M1-S, M1-650AG, M2, M2-S, and M2-650AG were selected from theabove-described test pieces, and tensile test pieces (parallel partdiameter of 6 mm, length between gauge points of 24 mm) conforming tothe standard test (ASTM E8) were produced based on the materialsproduced through the technique shown above. Tensile tests at roomtemperature (22° C.) were performed at N=3 on the tensile test pieces,and average values of the tensile strength and the breaking elongationwere obtained and shown in Table 3. From Table 3, a tensile strength of1,100 MPa or more and a breaking elongation of 5% or more were obtainedin all of the test pieces. Among these, it was confirmed that a tensilestrength of 1,500 MPa or more was obtained from the test pieces ofM1-650AG and M2-650AG.

TABLE 3 Alloy member Tensile strength (MPa) Breaking elongation (%) M11,264 31 M1-S 1,466 32 M1-650AG 1,796 5 M2 1,354 26 M2-S 1,450 36M2-650AG 1,832 6

Measurement of Wear Resistance

The Vickers hardness (load: 4.9 N, indentation time: 10 seconds) wasmeasured for the cross-sectional test pieces of the alloy membersproduced above. 5 points in the plane of each test piece were measured,and each average value was obtained and shown in Table 4. The hardnesswas based on a hardness of 550 HV required for wear resistant parts inresource mining environments and the like, and a hardness of 550 HV ormore was determined to be “acceptable” and a hardness less than 550 HVwas determined to be “unacceptable”. 550 HV is a value required forsecuring wear resistance, and is a numerical value that can besufficiently put into practical use in a normal environment. RegardingM1-LD650AG, M1-RM650AG, M2-LD650AG, and M2-RM650AG, the hardness wasmeasured separately for a remelted part or a padding part of a surfacelayer part and the inside, and the acceptance was determined by thehardness of the surface layer part where wear resistance is required.

Measurement of Corrosion Resistance

Immersion test pieces (25 mm long × 25 mm wide × 2 mm thick) forimmersion tests in boiling 10% sulfuric acid were collected from thealloy members produced above. An immersion test in boiling sulfuric acidis a test that is additionally performed especially for members used instrongly acidic atmospheres such as resource mining environments orchemical plants, and is performed for evaluating further enhancedcorrosion resistance. In the immersion test, the test area for each testpiece was 14.5 cm², a test equipment was a glass flask (capacity: 1,000mL) to which backflow water-cooled glass capacitor was connected, a testsolution was a 10% sulfuric acid aqueous solution (about 10 mL for 1 cm²of a surface area of each test piece). Regarding the test temperature,the weight reduction amount after immersion for 24 hours under boilingconditions was obtained and was used as an index of corrosion rate(mm/year) using an alloy density (8.04 g/cm³). In the evaluation of thecorrosion resistance, a corrosion rate of 5 mm/year or low in boilingsulfuric acid was determined to be “acceptable”, and a case where thecorrosion rate exceeded 5 mm/year was determined as “unacceptable”.Although the case where the corrosion rate exceeded 5 mm/year wasdetermined as “unacceptable”, it is a numerical value that can besufficiently put into practical use in a normal environment. The resultsof the above corrosion tests are also shown in Table 4.

TABLE 4 Alloy member Wear resistance Corrosion resistance Vickershardness (HV) Determination of acceptance Corrosion rate (mm/year) inboiling 10% sulfuric acid Determination of acceptance M1A 380Unacceptable 4.5 Acceptable M1-500AG 420 Unacceptable 4.5 AcceptableM1-600AG 560 Acceptable 3.0 Acceptable M1-650AG 580 Acceptable 2.2Acceptable M1-700AG 620 Acceptable 2.1 Acceptable M1-800AG 680Acceptable 4.0 Acceptable M1-900AG 550 Acceptable 9.5 Unacceptable M1-S450 Unacceptable 1.8 Acceptable M1-RM650AG (Surface) 580 (Inside) 510Acceptable- 3.0 Acceptable M1-LD650AG (Surface) 570 (Inside) 510Acceptable- 3.5 Acceptable M2 420 Unacceptable 1.2 Acceptable M2-500AG440 Unacceptable 1.4 Acceptable M2-600AG 560 Acceptable 1.7 AcceptableM2-650AG 570 Acceptable 1.9 Acceptable M2-700AG 620 Acceptable 1.9Acceptable M2-800AG 700 Acceptable 2.2 Acceptable M2-900AG 580Acceptable 6.5 Unacceptable M2-S 440 Unacceptable 0.4 AcceptableM2-RM650AG (Surface) 570 (Inside) 460 Acceptable- 2.3 AcceptableM2-LD650AG (Surface) 560 (Inside) 470 Acceptable- 2.5 Acceptable

The evaluation results of the test pieces and determination ofacceptance are shown in Table 4 and FIG. 10 . First, it was confirmedthat the alloy members M1 and M2 which were samples that had notundergone a heat treatment step had a hardness of less than 550 HV andare not suitable for application to an environment where high wearresistance is required. In addition, it was also confirmed that M1-S andM2-S that had undergone only a solution heat treatment similarly had ahardness of less than 550 HV. However, since M1-S and M2-S has a tensilestrength of 1,100 MPa or more and a breaking elongation of 10% or more,they can be sufficiently put into practical use in applications or siteswhere no high wear resistance is required. In addition, the alloymembers M1-500AG and M2-500AG basically showed the same characteristicsas those of M1 and M2, respectively. There was only a small change inhardness from M1 and M2 because ultrafine particles did notprecipitated, and the hardness was less than 550 HV. On the other hand,the alloy members M1-900AG and M2-900AG were unacceptable because thecorrosion rate exceeded 5 mm/year. It is thought that this is becauseultrafine particles are transformed into hexagonal precipitates, whichare coarse and have poor corrosion resistance, during an aging heattreatment at high temperature and are increased in size exceeding 50 nm.

On the other hand, it was demonstrated that the hardness of surfacelayers of other alloy members (examples) exceeded 550 HV which wasfavorable. In addition, the corrosion resistance was also suitablebecause it was well below the standard value of 5 mm/year. In addition,the relationship between the aging heat treatment temperature and thehardness is shown in FIG. 10 . It can be seen from the drawing that ahardness of 550 HV or more is obtained when the aging temperature is550° C. or higher and that the hardness tends to be maximum at near 800°C. In addition, regarding the remelted and reshaped members (M1-RM650AGand M2-RM650AG) and the surface layer-added and shaped members(M1-LD650AG and M2-LD650AG), new cured layers were obtained in surfacelayer parts and a structure composed of equiaxed crystals with excellentductility was maintained inside the members. It was confirmed that aductility of 20% or more was maintained inside these members and thatthese members are particularly suitable for applications, such as dies,requiring all of surface hardness, ductility, and toughness.

The above-described embodiments and examples have been described forassisting the understanding of the present invention, and the presentinvention is not limited to only the specific configuration described.For example, a part of a configuration of a certain embodiment can bereplaced with a configuration of another embodiment, and a configurationof a certain embodiment can be added to a configuration of the otherembodiment. That is, in the present invention, a part of theconfigurations of the embodiments or the examples of the presentspecification can be deleted and replaced with another configuration,and another configuration can be added thereto. By such adjustment ofembodiments, the alloy members disclosed in the present invention can beapplied to corrosion- and wear-resistant components widely used inindustrial fields, resource fields, chemical plants, and die members.

Reference Signs List

-   2 Parent phase structure-   3 Boundary part of microcell structure-   4 Dislocation-   5 Precipitate-   6 Ultrafine particle-   7 Parent phase crystal grain-   8 Minute particle-   10 Molten metal-   20 Alloy powder-   100 SLM Powder additive manufacturing device-   101 Shaped member-   102 Stage-   103 Base plate-   104 Powder supply container-   105 Alloy powder-   160 Recoater-   107 Powder bed (Layered powder)-   108 Laser oscillator-   109 Laser beam-   110 Galvanometer mirror-   111 Collection container for unmelted powder-   112 2D Slice-shaped solidification layer-   101 a Shaped member (inside)-   101 b Shaped member (surface layer)-   200 Powder additive manufacturing device-   201 Powder supply container-   203 Laser beam or electron beam-   204 Table-   205 Vice-   206 Laser head part-   303 Shaped member-   S10 Raw material powder production step-   S30 Additive manufacturing step-   S40 Solution heat treatment step-   S50 Removal step-   S60 Remelting and resolidifying step-   S65 Surface layer-adding and shaping step-   S70 Aging heat treatment step

1. A production method of an alloy member comprising: an additivemanufacturing step of forming a shaped member through an additivemanufacturing method using an alloy powder containing elements Co, Cr,Fe, Ni, and Ti each in a range of 5 atom% or more to 35 atom% or lessand containing Mo in a range exceeding 0 atom% and 8 atom% or less, theremainder being unavoidable impurities; and an aging heat treatment stepof holding the shaped member obtained through the additive manufacturingstep in a temperature range higher than 500° C. and lower than 900° C.in a state where a melt solidification structure is provided at least ina surface layer part.
 2. The production method of an alloy memberaccording to claim 1, the method comprising the following steps betweenthe additive manufacturing step and the aging heat treatment step: asolution heat treatment step of heating the shaped member formed throughthe additive manufacturing step and holding the shaped member in atemperature range of 1080° C. or more to 1180° C. or less; a coolingstep of cooling the shaped member after the solution heat treatmentstep, and then a remelting and resolidifying step of melting andsolidifying the surface layer part of the shaped member again.
 3. Theproduction method of an alloy member according to claim 1, the methodcomprising the following steps between the additive manufacturing stepand the aging heat treatment step: a solution heat treatment step ofheating the shaped member and holding the shaped member in a temperaturerange of 1080° C. or more to 1180° C. or less; a cooling step of coolingthe shaped member after the solution heat treatment step; and then asurface layer-adding and shaping step of forming a melt solidificationlayer on the surface layer part of the shaped member that has undergonethe cooling step, through the additive manufacturing method using thealloy powder.
 4. The production method of an alloy member according toclaim 1, wherein, in the additive manufacturing step, a heat source usedin the additive manufacturing method is a laser beam or an electronbeam.
 5. An alloy member comprising: elements Co, Cr, Fe, Ni, and Tieach in a range of 5 atom% or more to 35 atom% or less; Mo in a rangeexceeding 0 atom% and 8 atom% or less; and unavoidable impurities as aremainder, wherein the alloy member comprises a microcell structure withan average particle diameter of 10 µm or less at least in crystal grainsof a surface layer part, wherein a boundary part of the microcellstructure has a dislocation having a surface density higher than thatinside the microcell structure, and wherein ultrafine particles havingan average particle diameter of 50 nm or less are dispersed andprecipitate at least inside the microcell structure.
 6. The alloy memberaccording to claim 5, wherein Ti is concentrated at the boundary part ofthe microcell structure.
 7. The alloy member according to claim 5,wherein minute particles having an average particle diameter of 100 nmor less are dispersed and precipitate in parent phase crystal grainsinside the member which are located at an inner portion of the surfacelayer part.
 8. The alloy member according to claim 5, furthercomprising: a portion having a Vickers hardness of 550 HV or more.
 9. Aproduct using the alloy member according to claim
 5. 10. The productaccording to claim 9, wherein the product is any one of an impeller of afluid machine, a screw of an injection molding machine, and a die.